1. Field of the Invention
The present invention relates to a plasma generating device, and particularly, it relates to a plasma generating device for ion implantation wherein an ECR source using electron cyclotron resonance is used.
2. Description of the Related Art
FIG. 1 shows a perspective view of a conventional microwave ion source for an ion implanter.
In FIG. 1, a wave guide 1 having a ridge inside is connected to an electrical discharge case 2, and an dielectric window 3 for sealing vacuum is sandwiched between the guide 1 and the case 2. The electrical discharge case 2 comprises two electrical discharge electrodes 4a and 4b separately provided substantially at the center of the case 2 and dielectric spacers 5a and 5b sandwiching the electric discharge electrodes 4a and 4b. The center portion surrounded by the electric discharge electrodes 4a and 4b and the electric spacers 5a and 5b forms a plasma generating chamber. Further, the electric discharge case 2 is surrounded by a coil 6 with which a strong electromagnetic field is applied in the axial direction of FIG. 1.
In above explained plasma generating device, microwaves generated by a microwave generating source (not shown) such as a magnetron are transmitted by the wave guide 1 and led to the electrical discharge case 2 through the dielectric window 3. The microwaves generate a strong microwave electrical field to the plasma generating chamber formed between the dielectrics 4a and 4b, and the magnetic field generated by the coil 6 is applied in the direction perpendicular to the electrical field generated by the microwaves. In order to generate plasma in the plasma generating chamber, a gas is led to the plasma generating chamber through a gas tube (not shown), and a high density plasma is generated in the plasma generating chamber by the interaction of the microwave electrical field and the coil magnetic field. The ions in the plasma are drawn outside in the form of an ion beam 9 by applying a suitable voltage to an ion extraction electrode system 8.
In the conventional device as shown in FIG. 1, the coil 6 surrounds the entire plasma generating device, and thus the magnetic resistance is very large. Therefore, to provide a strong magnetic field at the plasma generating chamber, the cross-section of the coil must be remarkably enlarged, and this increase of the size of the coil causes a corresponding increase in the size of the entire plasma generating device.
Japanese Unexamined Patent Publication (Kokai) No. 60-133646, published on July 16, 1985 discloses a microwave ion source, but this is not related to an ECR source. Also, it is provided with a large magnet, and a dielectric window is exposed to plasma.